Self-contained pump system for airless spraying and the like



Jan. 30, 1968 G. s. LEVEY 3,366,066

SELF-CONTAINED PUMP SYSTEM FOR AIRLESS SPRAYING AND THE LIKE Filed Jan. 5, 1966 4 Sheets-Sheet 1 INVENTOR. GUSTAVE S. LEVEY ATTORNEYS (5. S. LEVEY SELF-CONTAINED PUMP SYSTEM FOR AIRLESS Jan. 30, 1968 SPRAYING AND THE LIKE 5, 1966 4 Sheets-Sheet 2 Filed Jan.

INVENTOR. GUSTAVE S. LEVEY ATTORNEYS Jan. 30, 1968 G. s. LEVEY 3,366,066

SELF-CONTAINED PUMP SYSTEM FOR AIRLESS SPRAYING AND THE LIKE Filed Jan. 5, 1966 4 Sheets-Sheet INVENTOR.

GUSTAVE S. LEVEY ATTORNEYS Jan. 30, 1968 G. s. LEVEY 3,366,056

SELF-CONTAINED PUMP SYSTEM FOR AIRLESS SPRAYING AND THE LIKE Filed Jan. 5, 1966 4 Sheets-Sheet 4 INVENTOR GUSTAVE S. LEVEY BY W /Z Z/VA KFAEE/A/GTOALPEAEA/E 6 60200 ATTORNEYS United States Patent 3,366,066 SELF-CONTAINED PUMP SYSTEM FOR AIRLESS SPRAYING AND THE LIKE Gustave S. Levey, Houston, Tex., assignor to The Spee- Flo Manufacturing Corporation, Houston, Tex., a corporation of Delaware Filed Jan. 5, 1966, Ser. No. 532,483 10 Claims. (Cl. 103-50) ABSTRACT OF THE DISCLOSURE A pneumatic transmission system including an air compressor and a compressed air motor operable to drive a liquid paint pump of the type adapted to supply an airless spray gun. The compressed air is delivered to the air motor without substantial loss of the heat of compression. The air motor operates throughout its power stroke at substantially constant air pressure and then exhausts to atmosphere. The temperature of the exhaust air is above the dew point and condensation does not occur. System efficiency is relatively high since the temperature of air in the air motor approaches the output temperature of the compressor. A modulating compressor unloader adjustably controls the compressor output pressure by throttling the compressor inlet. The unloader valve is urged toward its open position by the air entering the compressor so it operates smoothly and does not snap closed.

This invention relates generally to pneumatic power transmission systems and more particularly to an improved system for supplying paint or other liquid under pressure to an airless spray gun wherein a compressed air motor is used to drive the liquid pump.

A system incorporating the present invention provides improved efficiency so the power required, in a given installation, is substantially reduced.

In the airless spraying of liquid paints or the like it is necessary to be able to supply the liquid to the spray gun at any selected pressure generally within a pressure range of from one to three thousand pounds per square inch. The pressure on the paint and the size and shape of the spray nozzle are selected by the operator to produce the best pattern at the desired flow rate. It has been customary to utilize an air operated liquid pump which produces the high liquid pressures required when operated by a compressed air motor supplied through an adjustable pressure reducing valve from a reservoir or other source of air at a pressure of about one hundred pounds per square inch. Such pumps and motors utilize the principle of differential areas to deliver liquid at a relatively constant selected high pressure when operated by a supply of compressed air at a much lower substantially constant pressure. The air motor operated pump maintains the liquid under the selected pressure and operates intermittently in response to the intermittent triggering of the spray gun.

In industrial installations it has been customary to sup ply the paint pump with shop air usually available in industrial plants. In other instances, when electrical power is available with suflicient circuit capacity, electric motors have been utilized to drive an air compressor to supply the required compressed air. In still other instances, where shop air is not available and sufiicient electrical power capacity is not available internal combustion engines are used to supply the required power. In any such installations the general practice in the art has been to deliver the air from the compressor into a reservoir wherein the compressed air cools from its compressor delivery temperature to a temperature approaching the atmospheric 7 temperature. The air is then usually passed through a moisture separator for additional condensation removal.

This usually results in further cooling of the air. The air then passes through an adjustable pressure reducing valve, with further cooling, to the air motor. In such prior systems substantially all of the heat of compression is removed before the air reaches the motor.

In such systems it has been found that the power required to drive the compressor, even in systems supplying only one spray gun, is such that the electrical motor drive cannot be used on a typical volt l5 ampere circuit. Generally the minimum power requirement of these prior systems has been in the order of 19 to 22 amperes when operating at 110 volts. Consequently, the use of electric motors for airless spraying has been limited to locations where heavy duty circuifs are available or where limited spray capacity could be tolerated. Therefore, portable units have frequently required the use of gasoline engines to drive the compressor.

In these prior systems in which the heat of compresssion is removed from the air between the air compressor and the air motor, condensation problems often arise since the reduction of the pressure of the compressed air at the reducing valve and at the air motor produces further cooling of the air. In some instances of high ambient humidity freezing occurs and renders the system inoperative. Therefore, such systems have generally required the use of a condensate trap or other means to remove condensation. Such condensate traps also remove oil from the compressed air so it has generally been necessary to provide means to supply additional oil to the compressed air to provide lubrication for the air motor of the liquid pump. Where icing has nevertheless persisted because of high humidity conditions, it has been necessary to resort to reheaters to add heat to the air before entering the motor.

A pumping system incorporating the present invention provides a compressor driven by a suitable source of power such as an electric motor or gasoline engine, a liquid pump driven by an air motor of the piston and cylinder type and connecting means to directly deliver the compressed air from the compressor to the air motor. The system is arranged so that air leaving the compressor with the heatof compression is transferred directly to the pneumatically driven liquid pump with a minimum amount of heat loss so that the compressed air does not reduce in volume to any appreciable extent between the compressor and air motor. Consequently higher system efliciency results and it is possible to operate the compressor with less power. It has been found that by utilizing the compressed air with its heat of compression to drive the liquid pump the overall system efficiency is improved to a substantial extent. It has been found in actual practice that the improved efficiency of the present system makes it practical to power airless spray systems with normally available 110 volt 15 ampere capacity circuits. Prior systems, where the compressed air cools before delivery to the air motor, required current at a rate between 19 and 22 amperes when operating at similar output pressures and flow rates. This improvement in system efliciency provides the same advantages when internal combustion engines are used by reducing the engine size and fuel consumption required for a given output.

The use of the air with its heat of compression in the air motor eliminates the need of condensate removal from the compressed air since the temperature of the air at the exhaust of the air motor is maintained substantially above the dew point and normally at a temperature slightly above the atmospheric temperature. Further, the elimination of a requirement for removal of condensate from the compressed air eliminates the 0 need of a device for adding a lubricant into the compressed air delivered to the air motor and provides sufiicient lubrication for the air motor.

The system provides a compressor which compresses atmospheric air substantially adiabatically. Consequently, the compressed air leaving the compressor is at a relatively elevated temperature. This hot compressed air is directly delivered to the liquid pump air motor at a temperature relatively close to the delivery temperature from the compressor. In the air motor the compressed air is utilized to drive the paint pump at a substantially constant pressure without expansion in the motor. At the end of the stroke of the air motor the valve shifts and exhausts the compressed air to atmosphere. This blow-down of the compressed air to atmosphere does not completely reverse the adiabatic compression and the temperature of the exhaust air approaches and in many cases exceeds the atmospheric temperature.

In a preferred embodiment of this invention a novel modulating compressor unloader and regulator operates to throttle automatically the inlet air supplied to the compressor. This unloader senses compressor output pressure and permits the compressor to run continuously and smoothly, without abrupt on and off changes, while maintaining the selected output pressure substantially constant despite the necessarily intermittent operation of the spray gun.

It is an important object of this invention to provide a novel and improved pneumatic transmission system combining a compressor for adiabatically compressing atmospheric air containing water vapor, a pneumatic motor and conduit means for delivering the compressed air from the compressor to the motor, the rate of heat loss in the system being sufficiently low so that the temperature of the exhaust air from the motor is above the dew point and condensation does not occur.

It is another important object of this invention to provide a novel and improved pneumatic system according to the preceding object wherein the various elements of the system are arranged to radiate heat at sulficiently low rates so that the exhaust air leaving the pneumatic motor is at a temperature near the atmospheric temperature.

It is another important object of this invention to provide a pneumatic power transmission system according to either of the preceding objects wherein the conduit means for delivering the compressed air from the compressor to the pneumatic motor functions without substantial removal of either moisture or lubricant from the compressed air.

It is still another object of this invention to provide a pneumatic power transmission system including a combined compressor unloader and pressure regulator maintaining a smooth continuous operation of the compressor and a substantially constant selected pressure at the motor during intermittent operation of the motor.

It is still another object of this invention to provide a novel and improved pneumatically driven pumping system for an airless paint spray gun or the like which operates with sufficiently high overall efficiency to permit the operation of the system on conventional 15 ampere, 110 volt circuits.

Further objects and advantages will appear from the following description and drawings wherein:

FIGURE 1 is a perspective view of a pumping system incorporating this invention particularly suited for supplying high pressure liquid to an airless spray gun;

FIGURE 2 is another perspective view of the system of FIGURE 1 illustrating the arrangement of the compressor and motor drive;

FIGURE 3 is an enlarged fragmentary section partially in longitudinal section illustrating structural detail of the liquid pump shown in FIGURES 1 and 2;

FIGURE 4 is an enlarged fragmentary longitudinal section of the control valve for the liquid pump of FIG- URE 3;

FIGURE 5 is a schematic illustration of the complete pumping system; and

FIGURE 6 is an enlarged view, partially in section, of the modulating unloader.

The embodiment of this invention illustrated in the drawings is particularly suited for the pumping of paint and the like for airless spraying. Such airless spraying is accomplished by supplying the liquid at a relatively high constant pressure to an airless spray gun which operates to produce a finely divided spray by hydraulic atomization without the aid of air or other gas at the gun.

In FIGURES 1 and 2 the pumping system incorporating this invention is illustrated mounted upon a cart 10 having large wheels 11 journaled thereon so that it can be easily rolled from one location to another and even moved up and down stairways without difficulty. A handle 12 permits the user to move the cart with ease and a leg 13 (illustrated in FIGURE 1) permits the cart to be rested in the vertical position, as illustrated, when the unit is being stored or used.

A generally rectangular open ended housing 14 is provided to house an air compressor 16 and electric drive motor 17. A pulley 18 (illustrated in FIGURE 1) on the motor 17 is connected by a belt 19 to a drive pulley 21 on the compressor 16.

A pneumatically operated liquid pump 22 is vertically mounted on the cart 10 by a U-channel frame 23. The liquid pump 22 consists of two main assemblies. The upper assembly 24 includes a piston and cylinder air motor operable by compressed air to produce reciprocating movement and a lower liquid pumping assembly 26 which functions to pressurize the liquid. The air motor assembly 24 is supplied with compressed air from the compressor 16 through a hose 27 and control valve assembly 28. Liquid is drawn into the liquid pumping assembly 26 through an intake line 29 from a liquid supply container 31. The pressurized liquid is delivered from the liquid pump 26 to an airless spray gun 32 through a pressure line 33. The preferred airless spray gun is disclosed in United States Letter Patent No. 3,000,576, dated Sept. 19, 1961. The spray gun of this patent permits fine finishing and operation at lower liquid pressures than prior airless guns. However, other types of airless spray guns may be used when fine finishing is not required. The motor 17 is provided with a cord 34 so that it can be plugged into a standard electrical outlet in the vicinity where the spraying is to be done.

FIGURES 3 and 4 illustrate one form of pneumatically driven liquid pump which is suitable for use with this invention. The liquid pumping assembly 26 includes a main housing member 36 having a differential area piston assembly 48 reciprocable therein. A first packing gland 57 and a second packing gland 59, respectively, seal against a small diameter section 49 and a large diameter section 51 of the piston assembly 48. The glands cooperate with the housing 36 and piston assembly 48 to define an upper chamber 37 and a lower chamber 63. A check valve 46 allows liquid flow into the chamber 63 and a check valve 54 allows liquid flow from the chamber 63 to the chamber 37.

The illustrated structure provides for the delivery of liquid on both the up and down strokes of the piston assembly 48. On the upward stroke liquid is drawn into the chamber 63 past the check valve 46. During this operation the check valve 54 is closed. Since the piston section 51 has a larger effective area than the piston rod 49 the upward movement of the differential area piston assembly 48 results in a displacement of liquid in the chamber 37 and pumping of such displaced liquid out through a lateral exhaust passage 64 and up along a tubular support 66 to the output opening 67. The spray gun pressure line 33 is connected to the output opening 67 so liquid is delivered to the gun on this stroke. On the downward stroke the liquid Within the chamber 63 is displaced by the larger diameter piston section 51 and flows past the check valve 54 into the chamber 37. Because the quantity of liquid displaced from the chamber 63 to the chamber 37 is greater than the reduction in displacement by the piston assembly 48 in the chamber 37 liquid is also delivered to the spray gun 32 on the downstroke.

The pneumatic motor assembly 24 includes a cylinder assembly 74 and piston assembly 83 connected to drive the piston assembly 48 of the liquid pump. A piston head 82 on thepiston assembly 83 divides the cylinder into an upper chamber 77 and a lower chamber 81. When compressed air is admitted to the lower chamber 81 while the upper chamber 77 is vented to atmosphere upward movement occurs. Conversely when the opposite connections are provided downward movement results.

A control valve 107, best illustrated in FIGURE 4, is mounted in the control valve assembly to alternately connect the upper and lower chambers 77 and 81 to supply pressure and to exhaust. The control valve 107 is operated in response to movement of the piston assembly 83 by a lost motion connection mechanism 118. The proportions are arranged so that the valve 107 remains in one position until the piston assembly 83 reaches its extended position and then shifts almost instantaneously to reverse the connections to the cylinder 74. The valve 107 then remains in the shifted position until the retracted position is reached at which time it again rapidly shifts to reverse the connections.

When the valve is in the position illustrated in FIGURE 4 compressed air supplied through the hose 27, shutoff valve 117 (see FIGURE 2) and valve inlet 116 is delivered to the upper chamber 77 through the passage 119. In this position of the valve the lower chamber 81 is connected through the line 101 to the exhaust port 106. When the valve 107 moves down from the illustrated position the cylinder connections are reversed.

Spring loaded detents 111 cooperate with springs 124 and 128 to insure rapid shifting of the valve 107. With this structure a substantially unrestricted connection of compressed air is provided to the respective chambers 77 and 81 until the end of the stroke so no adiabatic expansion occurs. When the valve 107 shifts the compressed air in the air motor is directly vented to atmosphere so the temperature drop during expansion is smaller than it would be if adiabatic expansion Was provided. Also with this structure the output force of the piston assembly remains constant throughout each stroke so the liquid pressure developed remains constant.

The various elements are proportioned so that the pressure on the liquid is substantially the same on each stroke even though the effective area of the piston assembly 83 for one direction of movement is not the same as the effective area of the piston for movement in the other direction. This is achieved 'by properly balancing the effective areas of the piston assembly 83 and the differential areas of the differential area piston assembly 48.

FIGURE 5 schematically shows the entire pumping system. The electric motor '17 drives the compressor 16 which in the illustrated embodiment is a two cylinder single stage compressor having a crank shaft 131 which drives two pistons 132 and 133 through connecting rods 134. Atmospheric air enters through the modulating unloader 135 and is alternately drawn in through intake ports 136 and 137 and past automatic valves 138 and 139 to the respective cylinders 141 and 142. Similarly, the air is compressed in the cylinders on the upstroke of the respective pistons 132 and 133 and pumped past an automatic valve 143 into an exhaust chamber 144 at the output pressure of the compressor.

The compression of the air is substantially adiabatic, except for the heat absorbed and radiated by the compressor. In this specification and the appended claims the term adiabatic compression is intended to include compression of this type. After continuous operation the compressed air delivered by the compressor 16 may reach a temperature in the order of 290 F. or higher when the output pressure is in the order of pounds per square inch gauge.

The compressed air from the compression chamber 144 flows through a pressure line 148 to a T 149 one side of which is connected to a relief valve 151 and the other side of which is connected to a pressure line 152 leading to a second T 153. One side of the second T 153 connects through a third T 155 with the pressure hose 27 which in turn connects to the valve housing 28 through the fitting 117 and the manually operated shutoff valve 154. Preferably, an insulated handle 156 is provided on the shutoff valve 154 so that the operator will not be burned when the valve is operated. Also, it is preferable to utilize a high temperature hose 27 having substantial insulating qualities to minimize the heat loss from the compressed air as it flows therethrough.

Connected to the other side of the second T 153 is a pressure gauge 157 and connected to the third T 155 is a pressure line 146 which supplies the unloader 135 with air at system pressure.

Referring now to FIGURE 6, the modulating unloader 135 includes a main body 161 having a lateral threaded nipple 162 which is connected to the intake port of the compressor 16. Mounted within the housing 161 is a modulating valve 163 carried by an operating plunger 164 and movable into engagement with a valve seat 166. A spring 167 extends between retainers 181 and 182 and resiliently urges the valve 163 in a direction away from the seat 166 normally maintaining free flow into the unit through a filter 165, past the valve seat 166 and to the nipple 162. The retainer 181 seats against the body 161 and the retainer 182 seats against an adjusting nut 168 threaded on an operating rod 184. The force of the spring 167 is adjustable by threading the nut 168 in or out along the rod 184.

System pressure is admitted to the chamber 170 at the right end of the plunger 164 through the pressure line 146 (illustrated in FIGURE 5) which is threaded into a port 171 in the housing 161. When the pressure in the line 146 increases to a value sufficiently high to overcome the action of the spring 167, the plunger 164 and valve 163 move to the left toward the seated position of the valve illustrated in FIGURE 6. When this occurs the inlet is shut off so the compressor ceases to deliver additional compressed air even though it continues to run. When the pressure in the line 146 is below the desired pressure, the spring 167 produces a greater force than the compressed air acting on the plunger 164 and the valve 163 moves away from its seat 166 allowing intake air to flow through the unloader into the compressor.

When the valve 163 is in a throttling position or fully closed a vacuum occurs on its downstream side 172. Since substantially atmospheric pressure is always present upstream from the valve 163 the differential pressure across the valve produces a force augmenting the spring force in urging the valve toward its open position. This force increases as the valve approaches its seat. Therefore, the valve does not tend to snap closed but rather provides good flow regulation even at very low flow rates.

The setting of the adjusting nut 168 determines the output pressure which is maintained in the pneumatic motor. When the size of the spray nozzle, the viscosity of the paint being sprayed and the selected pressure are such as to require the maximum output of the compressor when the gun is triggered, the spring 167 maintains the valve 163 at or near its maximum .open position. When the trigger of the spray gun is released, abruptly stopping the flow of paint, the pressure in the air motor rises and rapidly moves the valve 163 to the left toward its closed position. As the valve approaches its seat the increasing pressure drop across the valve resists complete closing, so that without substantial hunting or chattering the valve reaches a position at which the amount of inlet air admitted to the compressor just balances the loss of pressure from leakage and from the cooling of the 'air trapped in the pressurized side of the motor.

In normal operation the spray gun is triggered or opened at the beginning of a pass across the work to be painted and the trigger is released and the gun closed at the end of each pass. The unloading valve 163 responds quickly to the opening or closing of the spray gun but in normal use seldom, if ever, closes completely, thus maintaining a smooth continuous operation of the compressor and its driving motor without abrupt changes in loading and power requirements such as are produced by an on-ofiE unloading action or pressure switch. When the spray gun is used with a smaller spray nozzle or with a lower liquid pressure the operation is substantially the same except that the valve 163 maintains some throttling of the inlet at all times.

The modulating unloader 135 eliminates the need for the separate pressure regulator required in prior systems between the reservoir and the air motor. Rapid response is achieved because the volume of compressed air in the system is small. Still further the need of a check valve between the compressor and air motor is eliminated since the unloader regulates properly even at low flow rates. Such a check valve would be required with a pilot operated unloader, since small amounts of leakage cause sulficient changes in system pressure to produce operation of the pilot valve and repeated cycling of the unloader. With the present system small rates of compressed air flow caused by leakage or by cooling merely hold the valve 163 open a small amount, without hunting or chattering, to maintain desired pressure.

As stated above, it is desirable that the conduit means connecting the compressor with the pneumatic motor, which conduit means includes the chamber 144, the hose 27 and the connecting piping, be constructed with a relatively small volume, both to minimize loss of the heat of compression of the compressed air and to insure prompt response and accurate regulation of the liquid pressure by the adjustable unloader 135. In the illustrated embodiment the volume of this conduit means is no greater than about the displacement volume of the pneumatic motor. This construction has been found to operate satisfactorily and to obtain an improvement of to in efiiciency over prior systems having a conventional sized receiver between the compressor and the motor. In such prior systems the total volume of the conduit means, including the receiver, is substantially more than the displacement volume of the motor and the compressed air reaching the motor is substantially at ambient atmospheric temperature. In order to regulate properly the liquid pressure such prior systems include a pressure regulator between the receiver and the motor in addition to an on-olf switch or unloader for the compressor.

The improved efiiciency of this invention makes it practical to use a 15 ampere, 110 volt supply circuit (or an equivalent circuit at a different voltage) for airless spraying. Also the manufacturing cost of the system is reduced since this invention eliminates the need for receivers, condensate traps and oilers and extra check valves and pressure regulators. Further, the problems of condensation and icing are overcome. In the preferred form of this invention the components are arranged so that in normal continuous operation the exhaust temperature is above atmospheric temperature. If required, insulation may be added to various parts of the system to reduce heat loss until this condition is reached.

Although a preferred embodiment of this invention is illustrated, it is to be understood that various modifications and rearrangements of parts may be resorted to without departing from the scope of the invention as defined in the following claims.

What is claimed is:

1. A pneumatic transmission system for use with atmospheric air containing water vapor and having a dew point temperature, comprising a compressor operable to compress said atmospheric air to a first pressure and first temperature each higher than atmospheric pressure and temperature, a pneumatic motor operable by compressed air to produce work without substantial expansion of such compressed air and operable thereafter to exhaust such compressed air to atmosphere, and conduit means connected to receive air from said compressor at said first pressure and temperature and deliver the same to said motor, said conduit means and said motor being constructed and arranged to maintain the water vapor content of said air and retain a sufficient amount of the heat of compression in said air so that the air exhausting from said motor has a temperature at least equal to said dew point temperature whereby vapor condensation does not occur at any location within said system.

2. A pneumatic transmission system as set forth in claim 1 wherein said exhaust temperature is at least equal to atmospheric temperature.

3. A pneumatic transmission system as set forth in claim 1 wherein said compressor operates to adiabatically compress the atmospheric air and supplies sufficient lubricant thereto during compression to lubricate said pneumatic motor, and said conduit means delivers said compressed air from said compressor to said pneumatic motor without removing any substantial amount of lubricant therefrom.

4. A pneumatic transmission system as set forth in claim 1 wherein said compressor includes modulating unloader means operable in response to compressor ourput pressure to control rate of compressor intake and reduce compressor output as the pressure of the compressed air delivered to said pneumatic motor approaches a predetermined selected value.

5. A pneumatic transmission system as set forth in claim 1 wherein said pneumatic motor includes a double acting piston and cylinder actuator with said piston and cylinder relatively movable with respect to each other between an extended position and a retracted position, and a control valve operable to selectively connect one side of said piston to said conduit means and the other side of said piston to atmosphere, said control valve operating in response to relative movement between said piston and cylinder to reverse such connections each time said actuator reaches one of said positions.

6. A pneumatic transmission system according to claim 1 in which said pneumatic motor includes piston and cylinder means having a predetermined displacement volume during each cycle of operation and said conduit means has a volume not substantially greater than said displacement volume.

7. A compressor system comprising a compressor having an inlet and an outlet, an unloader and pressure regulator providing a valve connected to said compressor inlet operable to throttle inlet flow thereto, adjustable means biasing said valve toward its open position, pressure operated means connected to said compressor outlet and biasing said valve toward a position closing off said inlet with a force directly proportional to the pressure in said outlet, said valve being arranged in said inlet so as to be additionally biased toward its open position by the pressure differential across said valve.

8. A liquid pumping system for an airless spray gun comprising a piston pump operable to pressurize and deliver liquid on each piston stroke, an air motor connected to drive said pump, an air compressor having an inlet to inspire atmospheric air and an outlet to deliver compressed air at a first pressure and first temperature each substantially higher than atmospheric pressure and temperature, conduit means connecting said compressor outlet with said air motor, said air motor and liquid pump cooperating to deliver liquid throughout each piston stroke of said liquid pump at a substantially constant liquid pressure which is substantially higher than the pressure of the compressed air delivered by said outlet and is a direct function thereof, and a combined liquid pressure regulator and unloader including a throttle valve in said compressor inlet, adjustable means biasing said throttle valve toward open position, and means responsive to the pressure in said outlet biasing said throttle valve toward closed position.

9. A pneumatic transmission system comprising pneumatically operated load means having a variable compressed air requirement, a compressor having an inlet and an outlet, conduit means connecting said compressor outlet with said load means, and a compressor unloade-r and pressure regulator including a valve in said compressor inlet, adjustable means biasing said valve toward open position, pressure operated means connected to said conduit means and biasing said valve toward a position closing off said inlet with a force directly proportional to the pressure in said conduit means, said valve being arranged in said inlet so as to be additionally biased toward open position by the pressure dilferential across said valve.

10. A pneumatic transmission system as set forth in claim 9 wherein said conduit means operates to deliver 10 compressed air from said compressor to said load means without substantial heat loss so that the temperature of compressed air delivered to said load means approaches the temperature at the output of said compressor.

References Cited UNITED STATES PATENTS 1,047,452 12/ 1912 Schottgen 1413 11 1,374,154 4/1921 Mueller 60-62 1,417,227 5/1922 Berner 60-62 2,120,546 6/1938 Burt 6014 2,486,982 11/1949 Rossman 60-62 3,052,444 9/ 1962 Kintner 25162 3,299,832 1/1967 Milne 25l62 X FOREIGN PATENTS 514 1910 Great Britain.

ROBERT M. WALKER, Primary Examiner. 

